A quick heads up for those interested in human evolutionary history : In Journal of Biogeography Grehan and Schwartz presents evidence for the hypothesis that the closest living relative of humans is the orangutan, and not the chimpanzee.

The phylogenetic tree of the relationship of these four apes would then look like figure B, rather than the usual one in figure A :

My own beautiful cladograms.

Their conclusion is based on morphological data, rather than molecular data (DNA), and they counter that the well-known percentages of DNA that humans share with other apes are "primitive retentions" (older traits with a deeper evolutionary past shared by a larger group of species). Humans share 98.4% with chimpanzees, 97.5% with gorillas, and 96.5% with orangutans.

The morphological data on which their study is based include features of anatomy, reproductive biology, and behavior. For example, among the great apes only humans and orangutans have thick tooth enamel, long hair, male facial hair, concealed ovulation, a preference for private, face-to-face mating, and an ability to construct shelters and beds.

No doubt this is going to cause a fair amount of debate in the scientific community. Which is great. Stay tuned.

Reference :
John R. Grehan and Jeffrey H. Schwartz (2009). Evolution of the second orangutan : phylogeny and biogeography of hominid origins Journal of Biogeography, in press.